# The Fall of a Giant. Chemical evolution of Enceladus, alias the Gaia Sausage

## TL;DR

This paper develops a chemical evolution model for Enceladus, the Gaia Sausage, revealing its star formation history, chemical properties, and impact on the Milky Way's evolution during a major merger event.

## Contribution

It provides the first detailed chemical evolution model for Enceladus, linking its properties to the Milky Way's star formation quenching history.

## Key findings

- Enceladus has a median stellar age of about 12.3 Gyr.
- The stellar mass of Enceladus at merger was approximately 5 billion solar masses.
- Merger events like Enceladus may have suppressed gas accretion in the Milky Way.

## Abstract

We present the first chemical evolution model for Enceladus, alias the Gaia Sausage, to investigate the star formation history of one of the most massive satellites accreted by the Milky Way during a major merger event. Our best chemical evolution model for Enceladus nicely fits the observed stellar [$\alpha$/Fe]-[Fe/H] chemical abundance trends, and reproduces the observed stellar metallicity distribution function, by assuming low star formation efficiency, fast infall time scale, and mild outflow intensity. We predict a median age for Enceladus stars $12.33^{+0.92}_{-1.36}$ Gyr, and - at the time of the merger with our Galaxy ($\approx10$ Gyr ago from Helmi et al.) - we predict for Enceladus a total stellar mass $M_{\star} \approx 5 \times 10^{9}\,\text{M}_{\odot}$. By looking at the predictions of our best model, we discuss that merger events between the Galaxy and systems like Enceladus may have inhibited the gas accretion onto the Galaxy disc at high redshifts, heating up the gas in the halo. This scenario could explain the extended period of quenching in the star formation activity of our Galaxy about 10 Gyr ago, which is predicted by Milky Way chemical evolution models, in order to reproduce the observed bimodality in [$\alpha$/Fe]-[Fe/H] between thick- and thin-disc stars.